The objective of this research project is to assess the factors responsible for differences in the substrate specificities among cytochrome P-450-dependent microsomal mixed-function oxidase systems (MFO) from various sources. Present work involves the purification of cytochrome P-450, cytochrome b5, NADPH-cytochrome P-450 reductase and NADH-cytochrome c reductase from rabbit pulmonary and hepatic microsomal fractions. Components of the MFO are being examined by UV-vis spectroscopy, electron paramagnetic resonance spectroscopy, SDS-gel electrophoresis, and by their activities in reconstituted systems. Structural and immunochemical properties of the enzymes are also being investigated. The long range objective of this work is to determine the influence of: 1) multiple forms of the enzymic components of the MFO system; 2) endogenous compounds, and 3) exogenous compounds (substrates, inducers and inhibitors) on the substrate specificities of MFO systems from different tissues and species.